Exposure to highly estrogenic substances can disrupt reproduction and increase cancer risk. Effects on bone metabolism and cardiovascular health also have been documented. Chemicals that are weakly estrogenic are widespread in the environment, including several pesticides and a variety of chemicals in plants. Health effects of these environmental estrogens are not known. As a first step in exploring this question biological effects of plant estrogens will be measured in postmenopausal women. Seventy volunteers will be recruited for the study. They will eat a diet high in soybeans, a food rich in plant estrogens. Urine, blood, and vaginal cells will be collected before and after the diet for measurement of several biological factors expected to change with low doses of estrogens. These include pituitary hormones, liver-produced plasma proteins, urinary calcium, and vaginal cell cytology. Planning and recruitment is underway. The dietary experiment will begin in the fall of 1987. If plant estrogens are found to be biologically active in postmenopausal women, further questions arise: (1) What effects do these chemicals have on other segments of the population: males, reproductively active women, and babies on soy formula? (2) Do effects of plant estrogens explain some of the differences in morbidity and mortality seen in vegetarians compared with nonvegetarians? (3) Can dietary changes be used in prevention or treatment of estrogen-related conditions? (4) Do other environmental estrogens (like pesticides) affect human health through estrogenic changes in human biology?